Combustor prechamber

ABSTRACT

A combustion liner for a gas turbine combustion apparatus has a prechamber for mixing of fuel and combustion air. Air enters the prechamber with a radially outward and tangential flow through a cylindrical swirler. The swirler is movable axially to reduce its axial length and thus the effective area of the swirler to control the primary air flow into the prechamber and on into the reaction zone of the combustion liner. Fuel is scoured off the outer wall of the prechamber and preferably vaporized by the air flowing with swirling movement from the air inlet to the reaction zone.

United States Patent Quinn June 3, 1975 COMBUSTOR PRECHAMBER 215mm7/1956 Golden U (10/3965 [75] Inventor: Ronald E. Quinn, Indianapolis.Ind. P E v C J H nmury .rummer t usar [73] Asslgnfie: General Mfnorscorpmat'm" Assistant Examiner--Robert E. Garrett Dem), Mlch- Attorney.Agent or FirmPaul Fitzpatrick [22] Filed: May I, 1974 211 Appl. No:465,754 [571 ABSTRACT A combustion liner for a gas turbine combustionappa- 521 US. CL H 60/3923; 60/3965; 60/3971; ratus has a prechamber formixing of fuel and combus' 60/7974 R tron air. Air enters the prechamberwith a radially out- [5 H Int Cl H FOZC 3/00; F020 7/22 ward andtangential flow through a cylindrical swirler. [58] Field 0 Search H60/3923v 39.65 3971 The swirler is movable axially to reduce its axial60/3974 R length and thus the effective area of the swirler to controlthe primary air flow into the prechamber and [56] References Cited onmto the reaction zone of the combustion liner. Fuel UNITED STATESPATENTS 1S scoured off the outer wall of the prechamber and q preferablyvaporized by the air flowing with swirling 51 22335 25 movement from theair inlet to the reaction zone. 2,698,050 12/1954 Bloomer et al. 60/39654 Claims, 2 Drawing Figures COMBUSTOR PRECHAMBER My invention isdirected to combustion apparatus for liquid fuel, particularly thoseused at relatively high pressures and rates of flow as compared toordinary fuel burners supplied with air at substantially atmosphericpressure. Examples of such pressurized combustion apparatuses are foundin gas turbine engines. In such engines, it is desirable in many casesto improve combustion so as to minimize the discharge of carbon,unburned hydrocarbons, carbon monoxide, and nitrogen oxides. One helpfultechnique in reducing emissions is thorough mixing of the fuel with airand evaporation of the liquid fuel prior to its entry into the reactionzone of the apparatus where combustion takes place.

Particularly where the energy rate output of the combustor varies over aconsiderable range, it may be nec essary to control the air flow so asto maintain a desired fuel-air ratio in the reaction zone. This fuel-airratio is commonly referred to as the equivalence ratio, which is thequotient of the actual fuel-air ratio divided by the stoichiometricfuel-air ratio. Prevaporization of fuel facilitates clean and completeburning with relatively low equivalence ratios which are conducive tolow formation of nitrogen oxides.

My invention is directed to a prechamber type of combustor, andparticularly to the prechamber itself. To summarize the principles of myinvention briefly, air is admitted to an annular prechamber through aswirler which delivers the air outwardly and circumferentially so thatthe air swirls along and scours the inner surface of the outer wall ofthe prechamber. This wall converges toward the outlet of the prechamber.At a point near its greatest diameter and downstream of the swirler,fuel is put on the wall to be picked off by the air flow and evaporatedas it flows into the combustion chamber. The swirler is of a type havinga constant cross section but of variable length so that the area forentrance of primary air may be varied in accordance with operatingconditions which determine the required amount of fuel. In this way, theequivalence ratio in the reaction zone of the combustor may be varied asdesired.

The principal objects of my invention are to improve combustion ofliquid fuels, to provide an improved prechamber for combustionapparatus, and to provide a prechamber having variable air flow butsubstantially constant flow characteristics as flow is varied. A furtherobject is to provide a prechamber having an annular air entrance with avariable-area radial outflow air swirler disposed in the entrance.

The nature of my invention and its advantages will be apparent to thoseskilled in the art from the succeeding detailed description of thepreferred embodiment of the invention.

FIG. 1 is an axial sectional view, with parts broken away, of acombustion liner including a prechamber embodying the invention.

FIG. 2 is an enlarged cross sectional view of the prechamber taken onthe broken surface indicated by the line 2-2 in FIG. 1.

Referring to FIG. 1, a combustion liner 2 may be installed in an enginehousing or combustion chamber outer case (not illustrated) to which airis supplied under pressure for combustion of fuel. Air may be suppliedin the usual manner by a compressor and may be heated in a regenerator.Such an installation may be similar to that described in Collman. etal., US. Pat. No. 3,267,674, Aug. 23, I966.

Fuel fed to the combustion chamber is burned in the air thus suppliedand the resulting combustion products are directed to a user, such theturbine of a gas turbine engine. Preferably. and as illustrated, thecombustion liner is of circular cross section. A liner wall 3 defines inflow sequence from the upstream end of the liner a prechamber 4, areaction or combustion zone 6. a dilution zone 7, and an outlet 8 forcombustion products. All except the prechamber may be of knownstructure. The liner is shown broken away, and in practice the lengthwili be greater than illustrated. Air enters the dilution zone 7 formixing with and cooling of the combustion products through dilution orsecondary air ports 10 in wall 3.

The prechamber wall 11 is ofa divergent-convergent configuration,beginning at the extreme upstream end with a guiding flange 12 fromwhich extends a flaring wall portion 14, followed by a converging wallportion 15 which terminates at a radial wall portion 16 defining theupstream end of the reaction zone. The entrance to the reaction zone isthrough a circular opening 18 in the radial wall portion 16. Opening I8is preferably of slightly smaller diameter than the downstream end ofthe prechamber to provide an annular baffle.

A support 19, which also serves as a pilot fuel tube, is fixedlyconnected to the liner wall 3 by suitable structure of the combustionapparatus, not illustrated. It is coaxial with the prechamber. Struts20, at least three in number, fixed to tube I9 extend outwardly tosupport a centerbody 22 which defines the inner boundary of an annularflow path through the prechamber. The downstream end of the eenterbodyconverges to an opening 23. A pilot fuel nozzle 24 suitably mounted onthe end of tubular support 19 contains suitable spray mechanism of knowntype to discharge a small quantity of fuel in a conical spray throughthe opening 18 into the reaction zone 6. This fuel is for maintenance offlame under low power conditions, or for starting the engine.

The forward portion of centerbody 22 constitutes a cylindrical guide 26.Guiding flange l2 and guide 26 provide support for an air swirlingcylinder 27. This cylinder comprises a downstream ring 28 slidable onthe exterior of guide 26 and an upstream ring 30 slidable on the innersurface of guiding flange 12. An annular row or set of radial outflowswirl vanes 31 extends between the rings 28 and 30. These vanes may bebrazed or otherwise fixed to the rings. the mode of construction of theswirler being immaterial to the present invention. As is clear from FIG.2, these vanes are of such shape as to deliver air radially outwardlyand with a considerable circumferential component of motion into theprechamber. The ring 30 may be integral with a spider 32 including arms34 and a hub 35. Hub 35 is slidably guided on the support 19. Asillustrated in FIG. 2, support 19 defines a conduit 36 for carrying fuelto the pilot nozzle 24. Support 19, which is fixed to centerbody 22, maybe considered to be part of the centerbody.

The air swirling cylinder 27 is illustrated in the ex treme position, toprovide maximum opening of the swirler and airflow. It may be moved tothe left as illustrated in FIG. 1, with ring 30 sliding in flange l2 andring 28 sliding on guide 26, whereupon the space between ring 28 and thechamber wall portion 14 lessens to reduce air flow. Means forreciprocating the swirler is indicated by a rod 38 fixed to the spider32.

The main fuel supply is conducted to the prechamber by a fuel line 39which enters a ring manifold 40 of semi-circular cross section brazed orotherwise fixed sealingly to the outer surface of the prechamber wall11. Fuel supplied to the manifold, ordinarily at a pressure onlyslightly higher than that of the air in the pre chamber. is delivered tothe interior surface of the prechamber walls through a ring of smallports 42. which may be directed somewhat tangentially and somewhatdownstream relative to the axis of the prechamber.

In operation of the combustion apparatus, the air under pressuresurrounding the liner 2 flows through spider 32 and swirl vanes 31 intothe prechamber 4, where it picks up the fuel supplied through ports 42.The air swirls downstream with the fuel through the an nular flow path44 defined between wall and centerbody 22. The air, which is heated bycompression and ordinarily by regeneration from the engine exhaust,evaporates the fuel and delivers it through the opening 18 into thereaction zone. Combustion may take place as is customary in prechambercombustors, the mixture of air and evaporating fuel burning readilywithout local hot spots such as would be due to combustion around fueldroplets in a fuel spray. The structure of the combustion and dilutionzones of the liner is not ex plained in detail. since it may beconventional. The hot combustion products from the reaction zone 6 aremixed with additional air delivered from the same source as thecombustion air. this dilution air being supplied through ports 10 andmixing as it flows from the liner through outlet 8 to a user. Forstarting the engine or maintaining the flame, a small amount of fuel maybe delivered by the pilot nozzle 24.

With a fixed area for entrance of primary combustion air, theequivalence ratio varies undesirably with changes in the operating levelofa combustor which accompany changes in power level of the engine inwhich it is used. To reduce the amount of primary combustion air. theswirling cylinder 27 may be moved leftward as illustrated in PK]. 1 fromthe position shown to throttle the air flow as desired.

It will be clear that this provides a means for throttling the air flowwithout changing the effective direction of flow or disturbing itsnatural tendency to scour the outer wall of the prechamber. The radiallyoutward swirling flow enhances this scouring tendency, and also tends tocentrifuge any unevaporated oil droplets toward the outer wall l4, 15.

The detailed description of the preferred embodi ment of the inventionfor the purpose of explaining the principles thereof is not to beconsidered as limiting or restricting the invention, since manymodifications may be made by the exercise of skill in the art.

l claim:

1. A combustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner defining. in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechambcrwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber,the air inlet extending circumferen tially and axially of the preehamberupstream of the Lil fuel delivering means; an air swirling andthrottling cylinder disposed across the said air inlet movable axiallyof the prechamber. the cylinder bearing a set of swirl vanes adapted todirect the air outwardly and circumferentially from the inlet into theprechamher, the area of the set Of swirl vanes being variable by axialmovement of the cylinder to vary primary air flow into the liner.

2. A combustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner defining, in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber;a centerbody defining with the prcchamber wall an annular flow pathleading from the inlet to the reaction Zone, the air inlet extendingcircumferentially and axially of the prechamber upstream of the fueldelivering means and centerbody; an air swirling and throttling cylinderdisposed across the said air inlet movable axially of the prechamber,the cylinder bearing a set of swirl vanes adapted to direct the airoutwardly and circumferentially from the inlet into the prechambcr, thearea of the set of swirl vanes being variable by axial movement of thecylinder to vary primary air flow into the liner.

3. A combustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner de fining, in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber;the prechamber wall being divergent at the air inlet and convergentthrough the downstream portion of the flow path; the air inlet extendingcircumferentially and axially of the prechamber upstream of the fueldelivering means; an air swirling and throttling cylinder disposedacross the said air inlet movable axially of the prechamber, thecylinder bear ing a set of swirl vanes adapted to direct the airoutwardly and circumferentially from the inlet into the prechamber, thearea of the set of swirl vanes being variable by axial movement of thecylinder to vary primary air flow into the liner.

4. A combustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner de fining, in flow sequence. a prechamber, a reaction zone, adilution zone, and an outlet for combustion products. the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber;a centerbody defining with the prechamber wall an annular flow pathleading from the inlet to the reaction Zone, the prechamber wall beingdivergent at the air inlet and convergent through the downstream portionof the flow path; the air inlet extending circumferentially and axiallyof the prechamber upstream of the fuel delivering means and centerbody;an air swirling and throttling cylinder movable 3,886,728 6 axially ofthe prcchumber guided 0n the prcchambcr area of the sct of swirl vanesbeing variable by lIXlill wall and the cenlerbody. the cylinder hearinga set of movement ofthc cylinder to vary primary air flow into swirlvanes adapted to dircct the air outwardly and cirthe liner.

cumfcrentiully from tho inlet into the prcchamhcr. the

1. A combustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner defining, in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber,the air inlet extending circumferentially and axially of the prechamberupstream of the fuel delivering means; an air swirling and throttlingcylinder disposed across the said air inlet movable axially of theprechamber, the cylinder bearing a set of swirl vanes adapted to directthe air outwardly and circumferentially from the inlet into theprechamber, the area of the set of swirl vanes being variable by axialmovement of the cylinder to vary primary air flow into the liner.
 1. Acombustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner defining, in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber,the air inlet extending circumferentially and axially of the prechamberupstream of the fuel delivering means; an air swirling and throttlingcylinder disposed across the said air inlet movable axially of theprechamber, the cylinder bearing a set of swirl vanes adapted to directthe air outwardly and circumferentially from the inlet into theprechamber, the area of the set of swirl vanes being variable by axialmovement of the cylinder to vary primary air flow into the liner.
 2. Acombustion liner for a gas turbine combustion apparatus or the likecomprising a wall extending from an upstream end to a downstream end ofthe liner defining, in flow sequence, a prechamber, a reaction zone, adilution zone, and an outlet for combustion products, the prechamberwall having a substantially circular cross section; means for deliveringfuel to the inner surface of the prechamber wall; means defining anannular radial outflow air inlet at the upstream end of the prechamber;a centerbody defining with the prechamber wall an annular flow pathleading from the inlet to the reaction zone; the air inlet extendingcircumferentially and axially of the prechamber upstream of the fueldelivering means and centerbody; an air swirling and throttling cylinderdisposed across the said air inlet movable axially of the prechamber,the cylinder bearing a set of swirl vanes adapted to direct the airoutwardly and circumferentially from the inlet into the prechamber, thearea of the set of swirl vanes being variable by axial movement of thecylinder to vary primary air flow into the liner.
 3. A combustion linerfor a gas turbine combustion apparatus or the like comprising a wallextending from an upstream end to a downstream end of the linerdefining, in flow sequence, a prechamber, a reaction zone, a dilutionzone, and an outlet for combustion products, the prechamber wall havinga substantially circular cross section; means for delivering fuel to theinner surface of the prechamber wall; means defining an annular radialoutflow air inlet at the upstream end of the prechamber; the prechamberwall being divergent at the air inlet and convergent through thedownstream portion of the flow path; the air inlet extendingcircumferentially and axially of the prechamber upstream of the fueldelivering means; an air swirling and throttling cylinder disposedacross the said air inlet movable axially of the prechamber, thecylinder bearing a set of swirl vanes adapted to direct the airoutwardly and circumferentially from the inlet into the prechamber, thearea of the set of swirl vanes being variable by axial movement of thecylinder to vary primary air flow into the liner.